At the time of manufacturing semiconductors, especially at the time of cleaning wafers, it is necessary to supply a highly pure fluid, for example, highly pure hydrochloric acid by a desired flow rate. Therefore, according to the prior art, a flow rate control device shown in FIG. 8, that is, a flow regulating valve is used to control the flow rate of fluid to be supplied.
FIG. 8 is a sectional view showing a flow rate control device of the prior art, such as disclosed in Japanese Unexamined Patent Publication No. 2004-162774. A housing 190 of the flow rate control device 100 is made of resin. On the outside of the housing 190, an inlet port 110 and an outlet port 120 for fluid are respectively arranged. The housing 190 includes a first chamber 210 communicated with an inlet port 110 and a second chamber 220 communicated with an outlet port 120. Between the first chamber 210 and the second chamber 220, a valve seat 310 and valve body 320, which corresponds to the valve seat 310, are arranged. As shown in the drawing, a diaphragm 410 is fixed to an upper end face of the valve body 320. Further, a spring 390 for pushing the valve body 320 against the valve seat 310 is attached to a lower end portion of the valve body 320.
On the opposite side of the second chamber 220 with respect to the diaphragm 410, that is, in an upper portion of the diaphragm 410, an airtightly closed pressure chamber 290 is formed. This pressure chamber 290 is communicated with a pressure introduction port 180 formed on the top face of the housing 190.
When air is introduced from the pressure introduction port 180, the pressure chamber 290 is pressurized and the diaphragm 410 pushes the valve body 320 downward against the spring 390. Due to the foregoing, the valve body 320 is separated from the valve seat 310 and fluid flows from the first chamber 210 into the second chamber 220 and is discharged from the outlet port 120. When the pressure of air introduced into the pressure introduction port 180 is adjusted, the distance the valve body 320 moves according to an action of the diaphragm 410 is controlled. Due to the foregoing, the flow rate of fluid discharged from the outlet port 120 can be adjusted.
However, a flow rate control device made of resin, which is disclosed in Japanese Unexamined Patent Publication No. 2004-162774, can adjust the flow rate of a fluid of ordinary temperature and normal pressure. Accordingly, when the flow rate control device is used to adjust the flow rate of fluid, over a long period of time, temperature and pressure of which are high, for example, to adjust the flow rate of steam, there is a possibility that a portion of the flow rate control device may be damaged. Especially, since the valve body of the flow rate control device is reciprocated in a fluid of high temperature and pressure. Therefore, the valve body and valve seat are parts that may become damaged due to a lack of durability. Even if there is a slight amount of damage in the valve body and/or the valve seat, the flow rate of fluid supplied by the flow rate control device may be greatly changed from a desired flow rate.
Further, in the flow rate control device disclosed in Japanese Unexamined Patent Publication No. 2004-162774, one face of the diaphragm is exposed to fluid, the flow rate of which must be adjusted and the other face of the diaphragm is exposed to fluid which is charged in the pressure chamber. Therefore, in the case where a flow rate of fluid of a high temperature and pressure is adjusted, for example, in the case where a flow rate of steam is adjusted, the fluid of a high temperature and pressure and the fluid charged in the pressure chamber are adjacent to each other via a single diaphragm, which is a relatively thin film. Accordingly, the diaphragm may become damaged.
The present invention has been accomplished in view of the above circumstances. An object of the present invention is to provide a flow rate control device capable of stably controlling flow rate even when a flow rate of fluid of high temperature and pressure, for example, steam is adjusted with the flow rate control device.